What Differnt Megapixel Numbers Mean When Comparing Cameras

Digital Trends has an online article comparing the Canon EOS Rebel T5 to the Nikon D3300.

The fact that the Nikon D3300 sports a 24MP APS-C sensor vs. the 18MP sensor used by the T5 makes this look like a very one-sided comparison, but what does that 6 megapixel difference really mean when comparing the two cameras?

Take a look at the maximum image size each camera is capable of producing.

The T5 can produce a 5184 x 3456 image.  The D3300 can produce a 6,000 x 4,000 image.  Those numbers appear to be closer than the 30% difference represented by the megapixel number.  Applying a little math, the D3300 image is 15% wider and 15% taller. 

If the D3300 image is only 15% larger, why is the megapixel count 30% greater?

It's because you have to increase size in two directions in order to keep the aspect ratio.  Increasing both height and width by 15% increases the surface area by 30%.


That raises the question: which number should be used when comparing the two cameras?  The 15% height/width increase or the 30% increase in surface area?

Personally, I'd go with the 15% increase for one simple reason: printing results.  Print sizes are usually compared based on width or height.  D3300 images can be printed at a size 15% wider than those produced by the T5. 

(To get the increase in printing width when comparing cameras with different megapixel counts, take the percentage the smaller number must be increased and then halve that result.)


The 15% number also makes sense when comparing the prices of the two cameras.  The T5 with kit lens costs $550.  The D3300 with a similar lens costs $650.

That amounts to an 18% increase in price.


Nikon seems to be admitting that it's 24MP sensor is only 15% better than the 18MP sensor in the T5.


Footnote:  Remember we're talking image size not sensor size.  The two cameras use the same size sensor.  The D3300 has a larger pixel count because it uses slightly smaller individual photosensors.  This allows it to produce images that are larger than produced by the T5 when viewed at the same resolution.